Frustrated Lewis pair

Acids and bases
Acceptor number Acid Acid–base reaction Acid–base homeostasis Acid strength Acidity function Amphoterism Base Buffer solutions Dissociation constant Donor number Equilibrium chemistry Extraction Hammett acidity function pH Proton affinity Self-ionization of water Titration Lewis acid catalysis Frustrated Lewis pair Chiral Lewis acid
Acid types
Brønsted–Lowry Lewis Mineral Organic Oxide Strong Superacids Weak Solid
Base types
Brønsted–Lowry Lewis Organic Oxide Strong Superbases Non-nucleophilic Weak
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A frustrated Lewis pair (FLP) is a compound or mixture containing a Lewis acid and a Lewis base that, because of steric hindrance, cannot combine to form a classical adduct.^[1] Many kinds of FLPs have been devised, and many simple substrates exhibit activation.^[2][3]

The discovery that some FLPs split H₂^[4] triggered a rapid growth of research into FLPs. Because of their "unquenched" reactivity, such systems are reactive toward substrates that can undergo heterolysis. For example, many FLPs split hydrogen molecules. Thus, a mixture of tricyclohexylphosphine (PCy₃) and tris(pentafluorophenyl)borane reacts with hydrogen to give the respective phosphonium and borate ions:

${\displaystyle {\ce {PCy3 + B(C6F5)3 + H2 -> [HPCy3]+ [HB(C6F5)3]-}}}$

This reactivity has been exploited to produce FLPs which catalyse hydrogenation reactions.^[5]